The composition dependent structure of glasses in the B2O3-GeO2 system will be measured by employing the method of neutron diffraction with Ge isotope substitution. This system is one of the few oxide glass-forming materials that comprises solely network-forming cations, and the local motifs in the pure component B2O3 and GeO2 glasses are rather different, i.e. BO3 planar triangles versus GeO4 tetrahedra, respectively. The B2O3-GeO2 system is therefore a prototype for investigating the effect of mixing different network forming cations. The neutron diffraction results will give detailed information on the coordination environments of both Ge and B, and will be combined with the results from other techniques in order to build a complete picture of the structure and how this affects the material properties.